In recent years, according to the high functionalization and the thinning of electronic devices such as portable-type information terminals or mobile phones, a miniaturized package called a CSP (Chip Size Package) is used also as a semiconductor package contained in the electronic device. Further, in recent years, an eWLP (Embedded Wafer Level Packaging) has been noticed as the process of fabricating the CSP, and this packaging has already been employed in the fabrication of some of the CSPs (see patent literatures 1 and 2, for example).
In the case of fabricating semiconductor packages according to the eWLP, it is necessary to use a substrate (supporting substrate) for supporting semiconductor chips from underneath thereof in the fabrication process. To this end, according to the fabricating method of the patent literature 1, an adhesive sheet having an adhesive layer on each of the both surfaces thereof is pasted on a substrate, and a plurality of semiconductor chips are mounted on the upper surface of the adhesive sheet. Next, the plurality of semiconductor chips on the adhesive sheet are collectively sealed by resin to thereby complete a resin portion containing the semiconductor chips. Next, the adhesive sheet is heated to expand the adhesive layer, whereby an adhesive force between the substrate and the adhesive layer is reduced and then the adhesive sheet and the substrate are separated. Then, the resin portion is stripped from the adhesive sheet and wiring layers etc. are formed on the surfaces of the semiconductor chips thus exposed. Thereafter, the resin portion is cut out to thereby dice the chips. According to the fabricating method of the patent literature 2, as a method of separating an adhesive sheet and a substrate, there is also proposed a method of constituting the substrate by copper and removing the substrate according to an etching process using ferric chloride aqueous solution etc.